Battery saving circuits are used to minimize power consumption, or average current drained, by periodically, rather than continuously, supplying power to a receiver. Presently known circuits operating in radio receivers, search for the presence of an RF (radio frequency) carrier, as seen in waveform 21 of FIG. 2 during a clear channel operation. If a carrier is found, the receive or search time is extended, from 60 milliseconds to 300 milliseconds, to permit a further search for a valid coded squelch signal (CSS), as seen in waveform 22. Examples of coded squelch signals are the tone-coded squelch (TPL) and digital-coded squelch (DPL) in Motorola products. (TPL and DPL are both Motorola trademarks.) Coded voice transmissions enable the unsquelching (or unmuting of the speaker) of only the radios having a code matching (or validating) the received CSS signal to provide private conversations with selected users on the same RF channel.
Such coded squelch operated battery savers have a significant disadvantage in that every receiver within a system is switched ON longer to enable detection of the CSS, whenever any transmission of a carrier signal occurs, regardless of which individual receiver is intended to be reached. In addition, even if the correct CSS signal is not detected, the OFF period for these coded conventional squelch operated battery savers remains the same, at 60 milliseconds, as the OFF period during receiver sampling for the carrier signal. Since the ON time has increased while the OFF time is unchanged, the duty cycle proportionately decreases, from 1-to-1 (50%) to 5-to-1 (17%). Hence, when there is such co-channel activity, demonstrated by the presence of a carrier signal, with the wrong CSS signal detected, current saving is decreased because of the smaller duty cycle.